When Should the U.S. Return A Child to a Country In Which Sharia Law Might Be Applied?

The Federal Court of Appeals for New York weighs in on whether a U.S. court must order a child returned to a "country of habitual residence" when that country is a signer, with the U.S. of the Hague Convention on child abduction, but which might possibly apply Sharia law to the adjudication of the custody dispute. Thanks and the usual hat tip to Prof.Volokh.